Expression of Cyclins and Cyclin-dependent Kinase Inhibitors in Granulosa Cells from Bovine Ovary

The regulation of granulosa cell proliferation is complex, and it is essential for normal follicular development in mammals. The aim of this study was to examine the expression of cyclins and their inhibitors in the granulosa cells of follicles at different developmental stages. Follicles were classified into three groups: oestrogen-inactive dominant follicles (EIDs), oestrogen-active dominant follicles (EADs) and pre-ovulatory follicles (POs). The expression of CCND2 (cyclin D2) mRNA was significantly higher in granulosa cells from EADs and POs than in those from EIDs. The expression of CCND3 (cyclin D3) mRNA was significantly higher in granulosa cells from EADs than in those from other follicles. CCND1 (cyclin D1), CCNE1 (cyclin E1) and CCNE2 (cyclin E2) mRNA expression did not differ among the different follicular stages. The expression of CDKN1A (p21(cip1) ) and CDKN1B (p27(kip1) ) mRNA was significantly higher in granulosa cells from EIDs and POs, respectively, than in those from other follicles. Expression of CDKN2D (p19(INK4d) ) mRNA did not differ among the different follicular stages. Taken together, our study suggested that cyclins and their inhibitors are associated with granulosa cell proliferation at specific follicular developmental stages.